Architectures for Sharing of Current Sources in an Implantable Medical Device

ABSTRACT

A group select matrix is added to an implantable stimulator device to allow current sources to be dedicated to particular groups of electrodes at a given time. The group select matrix can time multiplex the current sources to the different groups of electrodes to allow therapy pulses to be delivered at the various groups of electrodes in an interleaved fashion. Each of the groups of electrodes may be confined to a particular electrode array implantable at a particular non-overlapping location in a patient&#39;s body. A switch matrix can be used in conjunction with the group select matrix to provide further flexibility to couple the current sources to any of the electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional applicationSer. No. 13/485,416, filed May 31, 2012, which is a Non-Provisional ofU.S. Provisional Application Ser. No. 61/502,409, filed Jun. 29, 2011.Both of these applications are incorporated herein by reference, andpriority is claimed to both.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devices,and more particularly to improved current source architectures for animplantable neurostimulator.

BACKGROUND

Implantable neurostimulator devices are devices that generate anddeliver electrical stimuli to body nerves and tissues for the therapy ofvarious biological disorders, such as pacemakers to treat cardiacarrhythmia, defibrillators to treat cardiac fibrillation, cochlearstimulators to treat deafness, retinal stimulators to treat blindness,muscle stimulators to produce coordinated limb movement, spinal cordstimulators to treat chronic pain, cortical and deep brain stimulatorsto treat motor and psychological disorders, and other neural stimulatorsto treat urinary incontinence, sleep apnea, shoulder subluxation, etc.

FIGS. 1A and 1B shows a traditional Implantable Pulse Generator (IPG)100, which includes a biocompatible device case 30 formed of aconductive material such as titanium for example. The case 30 typicallyholds the circuitry and a battery necessary for the IPG 100 to function,although IPGs can also be powered via external RF energy and without abattery. The IPG 100 includes in this simple example an electrode array102 containing a linear arrangement of electrodes 106. The electrodes106 are carried on a flexible body 108, which also houses the individualelectrode leads 112 coupled to each electrode. In the illustratedembodiment, there are eight electrodes on array 102, labeled E₁-E₈,although the number of electrodes is application specific and thereforecan vary. Array 102 couples to case 30 using a lead connector 38, whichis fixed in a non-conductive header material 36 such as epoxy forexample. As is well known, the array 102 is implanted in an appropriatelocation in a patient to provide suitable simulative therapy, and iscoupled through the patient's tissue to the IPG 100, which may beimplanted somewhat distant from the location of the array.

As shown in FIG. 1B, the IPG 100 typically includes an electronicsubstrate assembly 14 including a printed circuit board (PCB) 16, alongwith various electronic components 20, such as microprocessors,integrated circuits, and capacitors mounted to the PCB 16. Two coils(more generally, antennas) are generally present in the IPG 100: atelemetry coil 13 used to transcutaneously transmit/receive data to/froman external controller (not shown); and a charging coil 18 fortranscutaneously charging or recharging the IPG's battery 26 using anexternal charger (also not shown).

A portion of circuitry 20 in the IPG 100 is dedicated to the provisionof therapeutic currents to the electrodes 106. Such currents aretypically provided by current sources 150, as shown in FIGS. 2A and 2B.In many current-source based architectures, some number of currentsources 150 are associated with a particular number of electrodes 106.For example, in FIG. 2A, it is seen that N electrodes E₁-E_(N) aresupported by N dedicated current sources 150 ₁-150 _(N). In thisexample, and as is known, the current sources 150 are programmable(programming signals not shown) to provide a current of a certainmagnitude and polarity to provide a particular therapeutic current tothe patient. For example, if source 150 ₂ is programmed to source a 5 mAcurrent, and source 150 ₃ is programmed to sink a 5 mA current, then 5mA of current would flow from anode E₂ to cathode E₃ through thepatient's tissue, R, hopefully with good therapeutic effect. Typicallysuch current is allowed to flow for a duration, thus defining a currentpulse, and such current pulses are typically applied to the patient witha given frequency. If the therapeutic effect is not good for thepatient, the electrodes chosen for stimulation, the magnitude of thecurrent they provide, their polarities, their durations, or theirfrequencies could be changed.

(FIG. 2A shows that each of the electrodes is tied to a decouplingcapacitor. As is well known, decoupling capacitors promote safety byprevent the direct injection of current form the IPG 100 into thepatient. For simplicity, decoupling capacitors are not shown insubsequent drawings, even though they are typically present in practicalimplementations).

FIG. 2B shows another example current source architecture using a switchmatrix 160. In this architecture, the switch matrix 160 is used to routecurrent from any of the sources 150 p to any of the electrodes E_(N).For example, if source 105 ₂ is programmed to source a 5 mA current, andsource 105 ₁ is programmed to sink a 5 mA current, and if source 150 ₂is coupled to electrode E2 by the switch matrix 160, and if source 150 ₁is connected to electrode E₃ by the switch matrix 160, then 5 mA ofcurrent would flow from anode E₂ to cathode E₃ through the patient'stissue, R. In this example, because any of the current sources 150 canbe connected to any of the electrodes, it is not strictly required thatthe number of electrodes (N) and the number of current sources (P) bethe same. In fact, because it would perhaps be rare to activate all Nelectrodes at once, it may be sensible to make P less than N, to reducethe number of sources 150 in the IPG architecture. This however may notbe the case, and the number of sources and electrodes could be equal(P=N). Although not shown, it should be understood that switch matrix160 would contains P×N switches, and as many control signals(C_(1,1)-C_(P,N)), to controllably interconnect all of the sources 150_(P) to any of the N electrodes. Further details of a suitable switchmatrix can be found in U.S. Patent Pub. U.S. Patent Publication2007/0038250, which is incorporated herein by reference.

The architecture of FIG. 2B, like the architecture of FIG. 2A, alsocomprises some number of current sources 150 (P) associated with aparticular number of electrodes 106 (N). Other more complicated currentarchitectures exist in the implantable stimulator art. See, e.g., theabove-incorporated '250 Publication. But again generally such approachesall require some number of current sources 150 to be associated with aparticular number of electrodes 106.

The inventor considers the association of numbers of current sources andelectrodes to be limiting because such architectures do not easily lendthemselves to scaling. As implantable stimulator systems become morecomplicated, greater numbers of electrodes will provide patients moreflexible therapeutic options. However, as the number of electrodesgrows, so too must the number of current sources according totraditional approaches discussed above. This is considered undesirableby the inventor, because current source circuitry—even when embodied onan integrated circuit—is relatively large and complicated. Newerarchitectural approaches are thus believed necessary by the inventor toenable the growth of more complicated implantable stimulator systems,and such new architectures are presented herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show an implantable pulse generator (IPG), and themanner in which an electrode array is coupled to the IPG in accordancewith the prior art.

FIGS. 2A and 2B show traditional current source architectures for an IPGin accordance with the prior art.

FIG. 3 shows an IPG in accordance with an embodiment of the invention inwhich a plurality of electrodes are grouped and provided at differentlocations in a patient.

FIGS. 4A and 4B show different current source architectures inaccordance with embodiments of the invention to support the IPG of FIG.3.

FIGS. 5, 6A and 6B show timing diagrams for operating the IPG of FIG. 3.

FIG. 7 shows logic for enabling the current source architecturesdescribed herein.

FIGS. 8A and 8B show alternative arrangements for grouping of electrodesin an IPG in accordance with embodiments of the invention.

DETAILED DESCRIPTION

FIG. 3 shows a more complicated IPG 200 which contains a higher numberof electrodes than that illustrated earlier, and which may be indicativeof the future progress of IPG technology. In the example shown, thereare three electrode arrays 102 ₁-102 ₃, each containing eightelectrodes, with electrodes E₁-E₈ on array 102 ₁, E₉-E₁₆ on array 102 ₂,and E₁₇-E₂₄ on array 102 ₃. Each of the arrays 102 couples to the IPG200 at a suitable lead connector 38 ₁-38 ₃, which lead connectors can bearranged in the header 36 in any convenient fashion. It should beunderstood that this is merely an example, and that different numbers ofarrays, and different numbers of electrodes on each array, could beused.

In this example, each of the arrays 102 ₁-102 ₃ comprises a group ofelectrodes that is implanted (or implantable) in a different location ina patient's body, thus allowing for the provision of complex stimulationpatterns and/or stimulation across a wider portion of the patient'sbody. For example, in a therapy designed to alleviate sciatica, Location1 for the Group 1 electrodes of array 102 ₁ (E₁-E₈) might comprise thepatient's right leg; Location 2 for the Group 2 electrodes of array 102₂ (E₉-E₁₆) the left leg; and Location 3 for the Group 3 electrodes ofarray 102 ₃ (E₁₇-E₂₄) the patient's spinal column. In a therapy designedto alleviate lower back pain, Location 1 of Group 1 might comprise theright side of a patient's spinal column; Location 2 of Group 2 the leftside of the spinal column; and Location 3 of Group 3 a central locationin the spinal column. Or each of Locations 1-3 may comprise differentportions of a patient's brain in a deep brain stimulation example. Theexact locations of each of the arrays, the number of electrodes in eacharray, and the particular therapies they provide, are not important tothe concepts discussed herein. It is preferred that the Locations arenon-overlapping in the patient's body.

As discussed in the Background section, conventional wisdom suggeststhat tripling the number of electrodes (from eight to 24 in thisexample) would require tripling the number of current sources in the IPG200 used to support those electrodes. This is because conventionalapproaches associate a number of current sources with a particularnumber of electrodes, and hence the two would scale. As noted earlier,the inventor finds this unfortunate given the complexity and size oftypical current course circuitry.

The present current source architecture diverges from this conventionalapproach by sharing current sources with an increased number ofelectrodes, such as is shown first in FIG. 4A. Consistent with FIG. 3,24 total electrodes are supported by the current source circuitry ofFIG. 4A, comprising three arrays 102 ₁-102 ₃ (e.g., Groups) present inthree different Locations in the body. FIG. 4A is somewhat similar tothe architecture of FIG. 2A discussed earlier, in that there is aone-to-one correspondence of current sources 150 to electrodes within agiven Group. For example, there are eight current sources 150, and eightelectrodes in each Group. New to FIG. 4A is a group select matrix 170.The group select matrix 170 allows current from the current sources 150to be sent to particular electrodes in each of the Groups. For example,current source 150 ₁ can send its current to electrode E₁ in Group 1, toE₉ in Group 2, and to E₁₇ in Group 3. Current source 150 ₂ can send itscurrent to E₂ in Group 1, to E₁₀ in Group 2, and E₁₈ in Group 3, etc.

Group control is enabled in this example by the use of three groupcontrol signals G1-G3. When G1 is asserted, switches (e.g., transistors)in the group switch matrix 170 are closed to respectively route thecurrent from each of the current sources 150 ₁-150 ₈ to Group 1electrodes E₁-E₈. (Of course, not all of the current sources 150 ₁-150 ₈may be programmed at a given moment to provide a current, and so currentwill not necessarily flow at an electrode E₁-E₈ merely because of theassertion of G1). When G2 is asserted, each of the current sources 150₁-150 ₈ are coupled to Group 2 electrodes E₉-E₁₆, and likewise when G3is asserted, each of the current sources 150 ₁-150 ₈ are coupled toGroup 3 electrodes E₁₇-E₂₄. Although shown as switches, it should beunderstood that the group switch matrix 170 may also comprise aplurality of multiplexers.

Assume electrode E₁₃ is to output 5 mA of current while electrode E₁₂ isto receive that 5 mA of current. In this example, source 150 ₅ isprogrammed to source 5 mA worth of current, source 150 ₄ is programmedto sink 5 mA of current, and group control signal G2 is asserted.

With this architecture, there is no need to scale the number of currentsources; for example, the number of current sources 150 in this exampleequals eight, even though 24 electrodes are supported. A fourth group ofelectrodes (e.g., E₂₅-E₃₂) could also be supported by these same eightcurrent sources, etc. This is of great benefit, and conserves currentsource resources with the IPG 200.

FIG. 4B shows another current source architecture employing a groupselect matrix 170. The architecture of FIG. 4B is somewhat similar tothe architecture of FIG. 2B discussed earlier in that it uses a switchmatrix 160 to associate P current sources 150 ₁-150 _(P) with a numberof switch matrix outputs equal to the number of electrodes (N=8) in eachGroup. The switch matrix 160 thus allows the current of any of thecurrent sources 150 ₁-150 _(P) to be presented at any of the switchmatrix 160 outputs, and the group select matrix 170 then routes thoseoutputs to particular electrodes in the selected group.

Assume again that electrode E₁₃ is to output 5 mA of current whileelectrode E₁₂ is to receive that 5 mA of current. In this example, anyof the P sources can be chosen to source and sink the current; assumethat source 150 ₁ will source the current, while source 150 ₂ will sinkthe current. Electrode control signals C_(1,5) and C_(2,4) are assertedto close the necessary switches (not shown) in the switch matrix 160 torespectively connect source 150 ₁ to the fifth switch matrix output, andsource 150 ₂ to the fourth switch matrix output. Then group controlsignal G2 is asserted to respectively route those switch matrix outputsto electrodes E₁₃ and E₁₂.

FIG. 5 shows examples of therapies that can be enabled using the currentsource architectures of FIGS. 4A or 4B. As before, three arrays ofelectrodes, defining three Groups, are used to provide therapy to threedifferent Locations in the patient. Assume that the therapiesappropriate at each of these Locations have already been determined. Forexample, assume that at Location 1 it has been determined to sourcecurrent from electrode E₃ and to sink that current from electrodes E₂and E₄, and to do so at particular magnitudes and durations t_(d) whichare unimportant for purposes of this example. Assume further that suchtherapy is to be provided at a frequency of f as shown. Assume furtherthat at Location 2 it has been determined to sink current from electrodeE₁₁ and to source that current from electrodes E₁₀ and E₁₂, again at afrequency of f. Assume still further that at Location 3 it has beendetermined to source current from electrode E₁₈ and to sink that currentfrom electrode E₁₉, again at a frequency of f.

If the architecture of FIG. 4A is used, such therapy can be delivered asshown in FIG. 5. As shown, the therapies at each of the Locations areinterleaved, so that the various therapies are non-overlapping. Thisallows the current sources 150 to be shared and activated in atime-multiplexed fashion, first being dedicated to provision of therapyat Location 1, then Location 2, then Location 3, and back to Location 1again, etc. Assume that the architecture of FIG. 4A is used, in whichthere is a one-to-one correspondence of current sources 150 ₁-150 ₈ toelectrodes within a given Group, i.e., at a particular Location. In thisinstance, current sources 150 ₂-150 ₄ are used to provide the therapy toelectrodes E₂-E₄ in Group 1/Location1. Notice that group control signalG1 is asserted during this time as shown in FIG. 5. Then later, forexample, after a recovery period t_(rp) as discussed further below,these same current sources 150 ₂-150 ₄ are used to provide therapy toelectrodes E₁₀-E₁₂ in Group 2/Location 2, but this time with groupcontrol signal G2 asserted. Again after another recovery period, two ofthese three same current sources 150 ₂-150 ₃ are used to provide thetherapy to electrodes E₁₈ and E₁₉ in Group 3/Location 3, but this timewith group control signal G3 asserted. To summarize, by interleaving thetherapy pulses at the different Groups/Locations, the current sources150 can be shared and do not have to be increased in number to supportthe increased number of electrodes.

As is well known, stimulation pulses such as those shown in FIG. 5 wouldnormally be followed by pulses of opposite polarity at the activatedelectrodes, and even thereafter additional steps may be taken to reducethe build-up of injected charge or to prepare for the provision of thenext stimulation pulse. Such portions of time may be referred togenerally as a recovery phase, and are shown in FIG. 5 as taking placeduring a time period t_(rp). It is preferable to not issue a nextstimulation pulse until the preceding recovery phase is completed. Thedetails of what occurs during the recovery phases are not shown in FIG.5 for simplicity.

The extent to which therapies at different Locations can be interleavedwill depend on several factors, such as the frequency f of simulation,the duration of the stimulation pulses t_(d), and the duration of therecovery periods t_(rp). For interleaving and sharing of current sourcesto occur as shown, these various timing periods should not be inconflict so that access to the current sources can be time multiplexed.

That being said, modifications can be made in the disclosed technique toaccommodate at least some potential conflicts. For example, as shown inFIG. 6A, it is seen that the frequency of the therapy provided to theelectrodes in Group 2/Location 2 is different (f₂) from the frequencyprovided at the electrodes in Group 1/Location 1 and Group 3/Location 3(f₁). This at times crates periods of conflict, t_(c), where the Group2/Location 2 stimulation may overlap with stimulation in otherGroups/Locations. For example, specifically shown in FIG. 6A is aconflict between Group 2/Location 2 and Group 1/Location 1, where bothof these Groups/Location would be calling for support from the samecurrent sources 150 ₂-150 ₄. In this circumstance, and assuming theconflict would not occur too often, the logic 250 in the IPG 200(discussed below with reference to FIG. 7) may decide to arbitrate theconflict by allowing only the Group 1/Location 1 electrodes access tothe desired current sources 150 ₂-150 ₄. In other words, the Group2/Location 2 electrodes would simply not be pulsed during the conflict,as represented by dotted lies in FIG. 6A. Again, assuming such conflictswill not occur frequently, occasionally missing a stimulation pulse at aGroup/Location should not materially affect patient therapy. Also, thedownside to such therapy gaps can be alleviated by alternating theGroups/Locations being allowed access to the current sources during aconflict, e.g., by enabling Group 1/Location 1 at a first instance ofconflict, Group 2/Location 2 at a second instance of conflict, Group1/Location 1 at a third instance of conflict, etc.

Conflicts of this type can also be resolved in different ways dependingon the current source architecture used. FIG. 6B shows the same conflictbetween Group 1/Location 1 and Group 2/Location 2 presented in FIG. 6A.However, here the logic 250 in the IPG resolves the conflict not bysharing current sources, but instead providing different current sourcesto Group 1/Location 1 and Group 2/Location 2. Of course, this assumes amore flexible architecture is used in which current sources can befreely assigned to particular electrodes, such as the architecture ofFIG. 4B employing a switch matrix 160. Recognizing the conflict, thelogic 250 assigns current sources 150 ₁, 150 ₅, and 150 ₆ to electrodesE₁₀, E₁₁, and E₁₂ in Group 2/Location 2, rather than the current sourcesthat might otherwise be expected (i.e., sources 150 ₂-150 ₄) which areinstead assigned to the electrodes in Group 1/Location 1. Note thatduring the conflict both group control signals G1 and G2 can beasserted. Note also that current sources 150 ₂-150 ₃ are also assignedto the electrodes in Group3/Location 3, which is possible because thereis no conflict between Group 1/Location 1 and Group 3/Location 3.

As noted above, control of the various current source architecturesdisclosed herein can be achieved by suitably programmed logic circuitry250, as shown in FIG. 7. Logic 250 in one example can comprise amicrocontroller, as is common in an IPG. While the microcontroller 250can implement many different IPG functions, as relevant here themicrocontroller is responsible for processing one or more stimulationprograms 255 dictating therapy for a patient, and for enabling thecurrent sources and groups accordingly. In one embedment, thestimulation program 255 comprises separate stimulation programs for eachGroup/Location, which specific programs may have been arrived at througha fitting procedure during which the patient expresses his preferencefor particular settings. As shown, the microcontroller 250 ultimatelyissues commands to the current source architecture at appropriate times,including enabling particular current sources 150, and specifying themagnitude, polarity, and duration of the current pulses. Also ultimatelyissued by the microcontroller 250 are the group control signals (G1, G2,etc.), which are received at the group select matrix 170. If the currentsource architecture employs a switching matrix 160 as shown anddescribed in FIG. 4B for example, the microcontroller 250 can also issuethe control signals for that matrix (C_(1,1)-C_(P,N)). To the extentthat the stimulation program 255 presents a conflict, such as thosediscussed earlier with respect to FIG. 6A and 6B, special arbitrationlogic 260 may be used to resolve the conflict, such as by skippingcertain stimulation pulses (FIG. 6A), rerouting alternative currentsources 150 if possible (FIG. 6B), or in other ways.

To this point it has been assumed that Groups/Locations of electrodescorrespond to particular arrays 102 coupled to the IPG. But this is notnecessarily the case, and groups of electrodes and their locations canbe established in other ways. For example, FIG. 8A shows a singleelectrode arrays having 24 electrodes, divided into three Groups ofeight. Each of these Groups corresponds to a different Location fortherapy, even though present on the same array 102, and thus this typeof electrode grouping arrangement can still benefit from the currentsource architectures described herein. For example, eight currentsources 150 can be employed if the architecture of FIG. 4A is used, or Pcurrent sources if the architecture of FIG. 4B is used. FIG. 8B showsanother example in which a plurality of arrays (102 ₁ and 102 ₂) aretreated as one Group of eight electrodes, even though such arrays wouldnot be at exactly the same location in the patient. Nonetheless, the 24electrodes present in FIG. 8B can be supported by eight current sources(FIG. 4A) or P current sources (FIG. 4B).

It should be understood that a “current source” comprises any type ofpower source capable of delivering a stimulation current to anelectrode, such as a constant current source, a constant voltage source,or combinations of such sources.

A “microcontroller” should be understood as any suitable logic circuit,whether integrated or not, or whether implemented in hardware orsoftware.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

What is claimed is:
 1. An implantable stimulator device, comprising: aplurality X of groups each comprising a plurality of electrodes; aplurality of current sources; and a group selection matrix receiving Xgroup control signals, each of the X group control signals forsimultaneously coupling the plurality of current sources to one of the Xgroups of the plurality of electrodes.
 2. The device of claim 1, whereinthere are a plurality N of electrodes in each of the X groups, and Ncurrent sources.
 3. The device of claim 1, further comprising aplurality of arrays each comprising one of the X groups of electrodes,wherein each array is implantable at a different location in a patient.4. The device of claim 1, further comprising an array, wherein all ofthe X groups of electrodes are located on the array.
 5. The device ofclaim 1, further comprising a plurality of arrays, and wherein at leastone of the X groups of electrodes is located on a plurality of thearrays.
 6. The device of claim 1, wherein the group selection matrixsimultaneously couples the plurality of current sources to only one ofthe X groups at a given time.
 7. The device of claim 1, wherein thegroup selection matrix simultaneously couples the plurality of currentsources to a first of the X groups at a first time and simultaneouslycouples the plurality of current sources to a second of the X groups ata second time.
 8. The device of claim 1, wherein each of the pluralityof electrodes in one of the X groups is not in any other of the Xgroups.
 9. The device of claim 1, wherein each of the X group controlsignals are asserted at X different times to simultaneously couple theplurality of current sources to each of the X groups at the X differenttimes.
 10. The device of claim 1, further comprising a microcontroller,wherein the microcontroller receives at least one stimulation programand is configured to enable the X group control signals in accordancewith the at least one stimulation program.
 11. An implantable stimulatordevice, comprising: a case; a plurality of arrays coupled to the case,wherein each array comprises a group of a plurality of N electrodesconfigured for implantation at a location in a patient; a plurality of Ncurrent sources inside the case; and a group selection matrix inside thecase controllable by a plurality of group control signals, each groupcontrol signal comprising a single signal specific to one of the groupsfor coupling each of the N current sources to one of the N electrodes inthat group.
 12. The device of claim 11, wherein each array couples tothe case at a connector.
 13. The device of claim 11, wherein theelectrodes are linearly arranged on each array.
 14. The device of claim11, wherein the group selection matrix couples each of the N currentsources to one of the N electrodes in only one group at a given time.15. The device of claim 11, further comprising a microcontroller insidethe case, wherein there are X groups, and wherein the microcontroller isconfigured to assert the plurality of group control signals to couplethe plurality of N current sources to one of the N electrodes in each ofthe X groups at X different times.
 16. The device of claim 11, whereineach of the N electrodes in a group appear only in that group.